| Summary: | Feeding is a complex process that is essential to an organism’s fitness. Individuals often show intraspecific variation when feeding, from utilizing different foraging habitats to targeting different prey. These individual differences in foraging strategies are important as they can directly affect fitness, population dynamics, behavioral flexibility, and ecosystem functioning. For several decades, intraspecific variation was largely ignored in biological studies, but, more recently, there has been a growing effort to understand the role of intraspecific variation in ecological and evolutionary processes. Phocids (true seals) are a widespread group of marine carnivores that exhibit a diversity of underwater foraging strategies. In this dissertation, I integrate field methods, bio-logging technologies, morphological and physiological sampling, and controlled feeding experiments to examine intraspecific variation and behavioral flexibility in the foraging strategies of seals. Specifically, I compare the at-sea foraging strategies of northern elephant seals (Mirounga angustirostris) across the species range and find that the species exhibits intraspecific variation across their range based on the interplay of life history, season, and geography. I also conduct a detailed analysis of the sex-specific foraging strategies of northern elephant seals, one of the most sexually dimorphic mammal species on the planet. My results reveal that male and female northern elephant seals have distinct foraging strategies and that intraspecific niche divergence helps maintain sexual dimorphism in this species. I then examine specific feeding (or prey capture) strategies used by seals and find that bearded (Erignathus barbatus), harbor (Phoca vitulina), Hawaiian monk (Neomonachus schauinslandi), ringed (Pusa hispida), and spotted seals (Phoca largha) have converged on two underwater strategies—biting and suction feeding, and these strategies are associated with different behaviors and kinematics. I also demonstrate that seals show intraspecific variation and behavioral flexibility in their use of these different strategies, with individuals switching behaviors and kinematics when targeting different prey. Cumulatively, the results of this dissertation reveal that intraspecific variation and behavioral flexibility are widespread in this group of marine carnivores, and this plasticity has likely contributed to the ability of seals to successfully occupy the role of top predators in marine ecosystems worldwide.
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